The present invention relates to a process for increasing the filling power of tobacco. More particularly, the present invention relates to a process for increasing the filling power of tobacco at a substantially constant moisture content, that is, without substantially increasing or decreasing the moisture content of the tobacco during treatment.
During curing, the moisture content of tobacco leaves is greatly reduced resulting in shrinkage of the leaf structure and a decrease in filling power. Additionally, the shredding or cutting techniques generally employed to convert the cured tobacco leaves into filler may result in some lamination and compression of tobacco, thereby decreasing the filling power even further. Many processes have been devised for increasing the filling power of cured tobacco for reasons well known in the art.
The heretofore known processes may be broadly characterized as involving penetration or impregnation of the tobacco with impregnants (blowing or puffing agents) which when removed during a subsequent expansion process step generate elevated pressure in and expand the tobacco.
Among the impregnants which have been employed are pressurized steam, air, water, volatile organic liquids, ammonia, carbon dioxide, combinations of ammonia and carbon dioxide and compounds capable of liberating a gas when subjected to chemical decomposition, as by heating. Among the means disclosed for removing the impregnant to expand the cell walls are a sudden reduction in pressure, freeze-drying, convection heating, radiant transfer (infrared), and the application of a microwave field.
While a number of the known processes may be employed to provide a satisfactory, expanded tobacco product, which may then be blended with an unexpanded tobacco and formed into cigarettes or the like, the known processes do possess certain disadvantages. The use of certain impregnants, such as volatile organic liquids (e.g., freon), which are foreign to tobacco, may not be completely satisfactory because some of the materials employed are not always desired as additives and the introduction, in considerable concentration, of such foreign materials presents the problem of removing the excess expansion agent after the treatment has been completed in order to avoid affecting aroma and other properties of the smoke. Moreover, aside from the aforementioned disadvantages, the use of such foreign materials adds to the overall cost of producing tobacco end products.
The use of water as the impregnant is known. The earlier of the reported processes employing water as the sole impregnant tend to produce a more satisfactory result with tobacco stem than with tobacco lamina filler. One belief was that the lamina cellular structure was difficult to impregnate and that, therefore, most of the water remained on the surface. This belief may have motivated some of those skilled in the art to try vacuum impregnation and longer bulking times. More recent processes employing water as the sole impregnant have been successful in substantially increasing the filling power of tobacco lamina filler. Typically, in these processes, filler having a specific initial moisture content is subjected to rapid and uniform heat transfer which produces an expanded and stiffened filler having a relatively low moisture content. These processes, which may be viewed as involving dehydration of the filler, represent a significant advance in the art, but do require the establishment of critical initial moisture contents, the establishment and maintenance of the critical heat transfer parameters required to produce an expanded and stiffened filler having the essential, drastically reduced, post-treatment moisture content, and are generally accompanied by a significant loss of alkaloids, which may, in certain instances, be highly desirable. Discoloration and charring can occur when the various process parameters are not properly maintained.
Surprisingly, it has now been discovered that moisture elimination is not required during heat treatment in order to increase the filling power of tobacco and that heat treating the tobacco at a substantially constant moisture content can actually enhance filling power gain without loss of alkaloids. Additionally, since evaporation of water is not involved, the filling power gain can be realized at a lower energy expenditure.